In Of Mice and Men, why did Steinbeck choose this particular diction?
Steinbeck uses the local dialect of the California ranch hands to make his novella seem more real and immediate to readers. By not paraphrasing and reporting back to us what the ranch hands have said, but instead using their own words, he transports us more fully into their lives. This helps us feel closer to them.
For example, the following dialogue between Slim and George helps convince us that Steinbeck really knows the lives of the characters he writes about, because he can speak their language:
"I gotta pair of punks on my team that don't know a barley bag from a blue ball. You guys ever bucked any barley?"
"Hell, yes," said George. "I ain't nothing to scream about, but that big bastard there can put up more grain alone than most pairs can."
Most of us probably don't know what a "blue ball" refers to, but it doesn't matter—we can pick up the gist of what Slim is saying about the incompetence of the "punks" on his team while at the same time feeling that we are actually eavesdropping on a real conversation.
It is also important to note that even while different characters speak in roughly the same dialect, Steinbeck also uses their words to help characterize them. Slim is a thoughtful, perceptive, and sensitive person, and that is reflected in his diction. For example, he uses poetic alliteration in the repeated "b" sounds when he says:
a barley bag from a blue ball. You guys ever bucked any barley?
There is a gentle, poetic rhythm to his speech.
In contrast, George's language is cruder and blunter, relying on curse words for emphasis. This, too, is consistent with his character.
In addition to the dialect, Steinbeck uses a narrative voice that is literary and polished to further connect with the reader.